Different weapons on armour provide different abilities.
Larger calibre weapons (75mm or more) are actually very good direct fire support weapons.
Mortar is good for indirect firepower - very crucial in providing closer range,quicker kabooms to clear areas and break lines.
40mm grenades have their special uses.
0.5cal is more for general fire suppression/assault and engagement of small targets up to 1+km?
25-30mm CGs are for reinforced/armoured targets.
There's no such thing as too much Firepower hehehe. Personally, there's only never enough of firepower.